Figure 2.

Model for induction of a Rappaport furrow directly by spindle midzone components. (a) At metaphase the two spindles are separate. (b) At anaphase the spindle midzones signal to the cortex (arrows), initiating formation of the two primary furrows. (c) As the spindles elongate and the astral microtubules grow out, a new zone of microtubule overlap is created in the center of the cell. This new midzone signals to the cortex (arrows) initiating the Rappaport furrow. This model predicts the formation of overlap microtubule structures in the cell center in the Rieder et al. experiment (3) that could be detected by tubulin staining of cells fixed in late anaphase/telophase.